I appreciate your helpfulness to ????, but don't yantras like this have to be consecrated to be effective?

Good point Pema Chophel. I suppose yantras especially should be consecrated. Though you can certainly hang deity pictures and prayers, after all that's basically what prayer flags are, yes? So perhaps the better option is buy a consecrated amulet to hang, or just hang a picture of any "public" deity that is known for protection against naga harm, e.g. garuda or vajrapani (or even the 21 Taras). As you know, good relationships with nagas are good, but they can be temperamental!
consecrated amulets: http://www.mahasiddha.org/store/Amulets.html

I agree with Clearbluesky's advice about protection against nagas.
Nagas are cool until they start causing you problems!
I think I have had problems with nagas for years without realizing it. But now the garuda practice I am doing is making the problem slowly go away.
So be careful with dealing with nagas.

Also for restoring the environment, preventing unseasonal weather, preventing floods, earthquakes, etc. Good for the health and wealth of the world at large as well as for those offering the puja. Naga confession (Lu shag) is especially good during this age of rapaciousness of all the earth's resources as well as all the pollution we dump into the environment. Where we live, fracking is very prevalent. I can't believe the Nagas like this.

People that come to our Naga pujas regularly say that the experience was very powerful for them. It's not uncommon for participants to say that they have seen Nagas during the puja, have seen snakes after the puja, or have dreamed of Nagas and/or snakes that night. The more connection to the puja and those celebrating the puja, the more effective is the result. Thus, in Tibetan Buddhism, people that request such pujas or to be remembered in such pujas typically make some kind of offering (incense, Naga medicine, the three sweets and three whites, flowers, money) in order to strengthen the ten-drel or auspicious connection with those doing the puja. Also, the more realized and powerful the celebrants of the puja, the more obvious (ngon) are the effects. (In Tbetan Buddhism, manifest [ngon] realization and manifest [ngon] accomplishment are very important concepts.)

Our group was instructed by Chatral Rinpoche's Sang-yum, Khandro Kamala, to do Naga puja very regularly, and the practice we do was given to us by Lama Dawa Chodrak. The more you do a puja like this, the more effective it becomes over time.